Investigating the Coke Formation Mechanism of H-ZSM-5 during Methanol Dehydration Using Operando UV–Raman Spectroscopy,ACS Catalysis

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Investigating the Coke Formation Mechanism of H-ZSM-5 during Methanol Dehydration Using Operando UV–Raman Spectroscopy
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-08-07 00:00:00 , DOI: 10.1021/acscatal.8b00928
Hongyu An _{1,

2} , Fei Zhang _{1,

2} , Zaihong Guan ₃ , Xuebin Liu ₃ , Fengtao Fan ₁ , Can Li ₁

Affiliation

Methanol dehydration on solid acid catalysts is a fundamental step in many industrial chemical processes, such as methanol to dimethyl ether (MTD) and methanol to olefin (MTO). The performance of catalysts often encounters the detrimental effect of coke deposition. However, the heterogeneous distribution of feedstock and product in a fixed-bed reactor usually brings in difficulties in the study of the coking mechanism. In this work, the coking progress of H-ZSM-5 in a fixed-bed reactor under MTD conditions is investigated using operando UV-Raman spectroscopy. Methylbenzenium carbenium ions (MB⁺), a key precursor for coke formation, was identified by UV resonance Raman spectroscopy and isotope exchange experiments. At higher temperature (473 K), MB⁺ rapidly transforms into “hard coke” at the beginning of the catalyst bed. The relative intensity of the 1605 cm^–1 peak can serve as an indicator for the catalyst deactivation. Moreover, water formed during MTD can suppress the transformation of MB⁺ into “hard coke” at the later parts of the bed. These results provide important information for the key steps and intermediates about coke formation on solid acid catalysts during methanol conversion, and the findings will contribute to improved catalytic performance in the related catalytic reaction.

中文翻译：

使用Operando紫外拉曼光谱研究H-ZSM-5甲醇脱水过程中焦炭形成机理

固体酸催化剂上的甲醇脱水是许多工业化学过程的基本步骤，例如甲醇制二甲醚（MTD）和甲醇制烯烃（MTO）。催化剂的性能经常遇到焦炭沉积的有害影响。然而，在固定床反应器中原料和产物的不均匀分布通常在焦化机理的研究中带来困难。在这项工作中，使用操作紫外拉曼光谱研究了MTD条件下H-ZSM-5在固定床反应器中的焦化过程。通过紫外共振拉曼光谱法和同位素交换实验鉴定了甲基苯碳铵离子（MB ⁺），这是形成焦炭的关键前体。在较高温度（473 K）下，MB ⁺在催化剂床层开始时迅速转变为“硬焦”。1605 cm ^–1峰的相对强度可以作为催化剂失活的指标。此外，MTD期间形成的水可以抑制MB ⁺在床层的后期转变为“硬焦”。这些结果为有关甲醇转化过程中固体酸催化剂上焦炭形成的关键步骤和中间体提供了重要信息，这些发现将有助于改善相关催化反应中的催化性能。

更新日期：2018-08-07

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